Spark gap and circuit therefor



Oct. 27, 1942. E. R.cAP|TA SPARK GAP AND CIRCUIT THEREFOR 2 Sheets-Sheet l Filed May 14, 1941 isA ORNEY ATT Oct. 27, 1942.

E. R. cAPl'rA 2,300,101 SPARK GAP AND CIRCUIT THEREFOR Filed may 14, 1941 2 sheets-sheet 2 ,INVENTOR Emil E. 'a/,dia

ATTORNEY Patented Oct. 27, 1942 UNITED STATES PATENT 2,3ll0,10l

OFFICE 14 Claims.

The present invention relates to an electric circuit and parts therefor, and more particularly to an electric circuit utilizing spark gaps and an improved spark gap therefor.

High frequency currents have been utilized in radio, stroboscopes, and in many industrial devices. For example, the heating of metal parts for case hardening, et cetera, is frequently done by exposing the part or a portion thereof to the field of a high frequency current, whereby heating currents are induced therein. In such industrial uses, substantial power requirements may be necessary to secure rapid heating. High frequency currents present many problems not encountered with low frequencies. These problems increase with the amount of power required and, as a result, it is not practical to generate the current direct from a mechanically driven generator. The practice is to utilize commercial direct or alternating current and to `increase greatly its frequency. This may be done with vacuum tubes or with spark gap circuits tuned for the frequency desired.

`There are advantages with spark gap circuits, particularly where substantial power is required; likewise, there are disadvantages. To secure good results, a number of spark gaps in series are desirable, sometimes fifty or more. The impedance of such a circuit is extremely high until the gaps strike, then the impedance becomes so low that the spark gap, in effect, becomes a short circuit. Where the power requirements are substantial, high voltages are desirable in the circuit in order to minimize heat losses and to prevent undue heating and damaging of insulation. With high frequency currents, the circuits should be resonant. Attempts to change the power output by changing the voltage, reactance or the length of the spark gap create complications.

The present invention aims to provide an improved circuit and an improved spark gap therefor which retain the advantages of spark gap circuits and at the same time minimize or eliminate the disadvantages noted above by facilitating the use of high voltages and by simplifying the controlof the circuits and the power output therefrom.

An object of the present invention is to provide an improved electric circuit or device for utilizing high frequency currents.

Another object of the invention is to provide an improved spark gap device for use in producing high frequency currents.

Another purpose of the invention is to ,Sim- .55

plify the regulation and control of a high frequency current produced by a spark gap.

Another object of the invention is to control the output of a high frequency circuit without changing the reactance of the circuit, or the distance between the spark gaps.

Another object of the invention is to provide a quench spark gap unit having a low inherent capacitance.

Another object of the invention is to provide a quench spark gap unit, which Will have a long life.

Another object of the invention is to provide a plurality of spark gaps having a total electrode capacitance not greater than three times the capacitance of the sparking surfaces.

Another object of the invention is to provide a high voltage spark gap circuit having a suiciently low capacitance to permit the use of higher voltages Without the spark gap striking.

Another object of theV invention is to provide an improved electric circuit for heating metal parts by induced high frequency currents.

Another object ofthe invention is to provide a spark gap device having a central member with sparking surfaces at its ends and adjustable end members having sparking surfaces cooperating With the sparking surfaces of the central member.

Other and further objects of the invention Will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

A preferred embodiment of the invention has been chosen for purposes 0f illustration and description and is shown in the accompanying drawings, forming a part of the specification, wherein Fig. 1 is a perspective viewof a preferred embodiment of a spark gap unit;

Fig. 2 is a longitudinal sectional view along the line 2-2 of Fig. l;

Fig. 3 is a sectional view along the line 3-3 of Fig. 2;

Fig. 4 is a sectional view along the line 4 4 of Fig. 2; and

Fig. 5 is a Wiring diagram of a high frequency power circuit with a preferred embodiment of auxiliary control circuit.

For convenience the improved spark gap will be described first and then the improved circuit, in which the spark gap is particularly useful, Will be explained.

Referring more particularly to Figs. l to 4 of the drawings, there is shown a spark gap unit having a base I molded of an insulating material such as Bakelite, rubber or the like, having suitable apertures 2 to permit the device to be bolted to any suitable panel for mounting the units singly or in banks. Suitable longitudinal slots 4 are provided in the base adjacent the ends thereof and a central slot 5 intermediate the two end slots. I rijhese slots serve to mount the units I2 at the ends of the device and the unit I4 centrally thereof, as will be described hereinafter. Each end of the support is provided with projections 3 having apertures 9 therethrough adapted to accommodate a threaded adjusting bolt I9. A nut I I intermediate the projections 8 which may be cemented in place, engages the threaded bolt and eliminates the necessity for threading the apertures 9. The bolts Ill serve to adjust the spark gaps by movements of the units I2 to and from the intermediate unit I 4 as will be described hereinafter.

The units I2 are identical in construction, and a description of one will suce. Likewise, the center unit I 4 is identical with the end units except that it is not adjustably mounted and except that it has two sparking surfaces Where the respective end units have only one. Referring to either one of the end units I2, the substantially cylindrical member 6 is preferably made of metal and has one end closed by a metal disc I5, preferably copper, brazed in position and a second disc I6, preferably tungsten, welded thereto. The opposite end of the member I2 may be closed by a disc I'I brazed or othe-rwise held in position. A pair of tubes I8 and I9 are secured into apertures in the member in any suitable manner and extend upwardly suciently far therein to provide a water level in the chamber. Water preferably flows into the chamber through the tube I 8 and out through the tube I9. The tubes I8 and I9 extend through the slots 4 in the insulator base I and also through a block Ztl operatively secured to the end of the bolt I8. Thus, when the bolt I9 is rotated for adjustment, the unit I2 attached thereto by means of one of the blocks 28 is moved to and from the central unit I4. A stud 2l (Figs. 2 and 4) may be soldered or ,welded to the member 6 to extend dowpwardly from the central part thereof and may be provided with a threaded bore 22 therein to receive a screw 24. A spring 25 through the intermediation of the screw 24 resiliently holds the members 6 and the units I2 in engagement with the projections 3 on the upper side of the support I.

As indicated above, the end units I2 may be the same in every respect both as to their mounting and construction. The middle unit I4, in the preferred embodiment, differs from the end units in having no adjustment and in having a disc I5 brazed in each of its ends with tungsten members or discs I9 welded or otherwise secured thereto. It will be understood that various types of materials may be used and that the construction and shape of the chambers may be varied within wide limits. Preferably the electrical terminals of the unit are connected at 2'I on the tubes I3 and I9 of the end units. A suitable rubber hose (not shown) may be connected to the tube I8 of the first unit for supplying water or similar liquid thereto. Another hose may be connected between the tube I 8 of an end unit I2 and the tube I8 of the central unit I4 to deliver water from the end unit to the central unit. The tube I9 of the central unit may be connected to the tube I 8 of the other end unit to deliver water from the central unit to the other end unit. A rubber hose connected to the tube I9 of the end unit carries the Water away to a suitable drain. In this Way, water may be passed through the three units. The water columns should be sufliciently long so that the current will not by-pass through the water. The tubes being brazed or otherwise secured into the metal member 6, the current will pass freely from the terminals 2l through the member 6 to the sparking surface I6.

An important feature of the unit is its simplicity and adjustability and particularly the low capacitance of the gaps. The discs I5 and I6 are relatively small and thin as compared to the cumbersome discs heretofore used with fins and other metal parts for dissipating the heat of quench gaps. With the unit described herein, the flow of water effectively insures rapid cooling of the gap while the capacitance of the gap may be kept small.

It has been found that the inherent capacitance of the present gap is about one-fifth that of prior gaps, which enables a much higher voltage to be used without undesirable striking as will be described hereinafter. In addition, it is possible to prevent a substantial increase in the temperatures of the gaps and particularly in the member 6, thereby eliminating or greatly minimizing the variation of the spark gap occasioned by expansion and contraction of the parts which would result from substantial temperature changes.

Referring more particularly to Fig. 5, illustrating an improved circuit utilizing the spark gap units described above, there is shown the main power circuit 3!! at the right of the drawings with an auxiliary circuit 3| at the lower left side of the drawings. For convenience, the main power circuit will be described rst. Low frequency current (usually sixty cycle) may be delivered to and through leads 34, 35 and double pole switch St to the primary 3l of a transformer 38 which preferably increases the voltage substantially and delivers the current through the secondary 39 thereof. One side of the secondary 39 is connected through wire 34a, resistance 49, wire 34h, condenser 4I, variable inductance 42 and wire 34e to a variable position on the coil 44 of the output circuit 45. The other side of the secondary 39 of the transformer 38 is connected to the output circuit 45 through wires 35a, resistance 49a, wire 35D, condenser 4Ia, variable inductance 42a., wire 35e to a variable tap on the coil 44 of the output circuit 45.

A series of spark gaps 4l, preferably of the type described herein, are provided intermediate the wires 34h and 35h. The resistance 40 and 49a are for dampening purposes to protect the windings of the transformer 38 when the spark gaps 41 strike. The condensers 4I and 4Ia are for the purpose of blocking the low frequency current and passing the high frequency current. The variable inductances 42 and 42a are for the purpose of tuning the spark gap circuit to the proper frequency for resonance with the work circuit formed by the coil 44 and condensers 5t. Preferably the inductances 42 and 42a are correspondingly adjusted to provide a balanced circuit, that is, a circuit with substantially the same impedance in the respective sides thereof.

When the switch B is closed and after the conditions of the circuit are such that the spark gap 41 strikes, a current of the tuned frequency of the circuit will be delivered to the coil 44 of the output circuit 45. The amount of power delivered t the output circuit maybe controlled vby varying the rate that the spark gap strikes.

The energy delivered by a spark gap circuit depends upon the number of strikes of the spark gap and the intensity thereof.

As will be understood by those skilled in the art, when the voltage supplied by the transformer 38 is sufficiently great to break down the spark gap 41 power will be supplied to the output circuit 45. The amount of power supplied can be regulated within limits by changing the characteristics of the circuit. However, in circuits of this type, it is particularly desirable to have the circuit balanced to avoid propagating waves which will interfere with radio sets in the neigh borhood. Hence, changes in the inductance or capacity of the circuit tend to create complications. Further, a high voltage is desirable in the spark gap circuit in order to minimize the heat losses therein. In addition, it is desirable to control the power output without unbalancing the circuit. For this purpose, an auxiliary circuit 3l has been provided which will now be described.

Leads or wires 5| and 52 connect with the power lines 34 and 35 through switch 36. The wire 5l connects directly with one side of the primary 54 of a transformer 55. the other side of the primary of the transformer through a rheostat 56. One side of the secondary 51 of the transformer is connected through wire 5Ia and condenser 58 to one side of the coil of transformer 59. The other side of the secondary 51 is connected through the wire 52a and the condenser 58a to the other side of the coil transformer 59. A suitable spark gap 60 is provided between the wires Sla and 52a, preferably two air cooled adjustable spark gaps are utilized. The coil 59 is inductively connected to a coil 60, which may be a Tesla transformer, and continues through wire 52b condenser 6I to a terminal 62 spaced slightly from or `touching the spark gaps 41.

Referring to the auxiliary circuit 3|, when the switch 36 is closed, low frequency current is conducted through the wires 5I, 52 to the primary of the transformer 55. The spark gap 60 creates a high frequency current, the voltage of which is greatly increased by the coils 59 and 60. When the terminal 62 is placed near or in contact with the center of the series of spark gaps 41 this high voltage current tends to flow through the spark gap 41 and pass to the secondary of the transformer 39 through Wire 34h resistance 43 and wire 34a. The inherent capacitance between the windings of transformer 38 permits the high frequency current to pass from wire 34a to wire 34 and thence through wire 5|, wire 5|c condenser 65 to the other side of the transformer coil 59. Hence, the auxiliary circuit with its high voltage will cause the spark gap 41 to strike, regardless of whether or not the voltage in the main circuit, that is, between wire 34h and 35h is suiiicient to make the gaps strike. The ionizing function of the auxiliary circuit may also be acl complished by other electrical means, for example, a vacuum tube oscillator or a mechanical current making and breaking device. gap has struck and the air in the gaps ionized, the lower voltage in Athe main circuit is sufficient to cause the current of the main circuit to flow through the gaps. Hence, a voltage may be selected for the main power circuit which is most The wire 52 connects with Once the 1 coil or transformer 44.

ments.

desirable from an operating standpoint and without being limited to the voltage required to cause the spark gap 41 to strike. Further, since the spark gap 41 is of the quench type, a spark will be quenched immediately, and will not strike again unless there is sufficient voltage therefor. The spark gaps 41 will strike only when the spark gaps 60 in the auxiliary circuit strike. Hence, the periodicity of the spark gaps 41 may be controlled by regulation of the periodicity of the spark gap 60. The latter may be controlled by adjustment of the rheostat 56 in the primary circuit of the transformer 55. Since the power output depends upon the periodicity of the spark gap, the main power output may be controlled through the auxiliary circuit without changing the elements in the main power circuit. If desired, other means may be utilized for controlling the periodicity of the auxiliary spark gap 60. By utilizing an auxiliary circuit to controlthe striking of the spark gaps 41, the voltage in the main circuit may be fixed within much Wider limits than would be possible otherwise.

In a spark gap the striking voltage depends in a large measure on the inherent capacitance n a suitable panel to form a bank of gaps in series.

The adjusting bolts l0 at the end of each unit may be used for adjusting the gaps as desired. Thereafter, the gap is placed in a suitable circuit, for example, at 41 in the circuit of Fig. 5. Whenthe switch 36 in Fig. 5 is closed, low frequency current is delivered to the transformer 38 and imposed upon the spark gaps 41. The spark gap circuit being tuned, high frequency current is delivered to the work circuit 46 through the 'I'hetaps on the coil 44 permit the wires 34e and 35e to be connected so that the circuit is balanced. If a piece of metal is placed in the eld of the coil 44 it may be heated to a red heat in a few seconds, so

. effective are the currents induced in the metal so much more rapidly, the induced current will heat the metal almost instantaneously.

The auxiliary circuit 3l applies a high voltage to the spark gap 41 through the transformer 59 and 60 energized by the auxiliary spark gap circuit. By controlling the auxiliary circuit which may not use more than ten or fifteen watts `of power. The main circuits, which may use or more kilowatts of energy, may be controlled. The auxiliary control is superior to present types of known controls.

It will be' seen that the present invention provides an improved quench spark gap device having a low inherent capacitance. The deviceis simple and is particularly adapted for high frequency circuits with substantial power require- The spark gap devices are easy to adjust, effectively cooled and may be used in high voltage circuits without undesired striking. The improved circuit permits the control of a main power circuit by an auxiliary circuit effective" on the main spark gap to control the power output without requiring adjustments inthe reactance of the main power circuit.

It will be understood that the invention is not limited to the power circuit described but may be used with any circuit where current at a relaively high voltage is broken.

As various other changes may be made in the form, construction and arrangement of the parts herein without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein isto be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a spark gap device, the combination of a base, a fixed member mounted on said base and .having sparking surfaces at its respective ends, an adjustable member mounted on said base at one end of said xed member, a second adjustable member mounted on said base at the other end of said xed member, each of said adjustable members having a sparking surface adjacent a sparking surface on said xed member, screw means operatively connected to each of said adjustable members to propel and retract said adjustable members toward and from said fixed member by turning said screw means, and metal tubesin heat conducting relation to said fixed and adjustable members for conducting cooling water to cool said members.

2. A liquid -cooled adjustable quench gap, having a total electrode capacitance not substantially greater than the capacitance between the sparking surfaces, comprising a pair of substantially parallel surfaces of substantial area, means for flowing a liquid for cooling said surfaces, means for retaining said surfaces in parallel relaticn, and means for moving the surfaces toward each other without distrubing their parallcl relation t decrease the space between the surfaces.

`3. A liquid cooled adjustable quench gap comprising a pair of substantially parallel surfaces of substantial area, means for flowing a liquid for cooling said surfaces, means for movably retaining said surfaces in parallel relation and screw means adapted to be turned to propel the surfaces toward each other without disturbing their parallel relation thereby to control the quenching characteristics of the gap.

4. In a' quench gap device, the combination of a support made of an insulating material, a plurality of aligned chambers resting on said support, one cf said chambers being fixed in position and other chambers being adjustable to vary their positions with respect to the xed chamber, spark gap surfaces on the respective ends of the xed chamber, spark gap surfaces on the ends of the adjacent chambers retained by said support in substantially parallel relation to the sparking surfaces on the xed chamber, and

means for flowing a cooling uid through saidl chambers.

5. In a device of the class described, the combination of a source of voltage, a power circuit connected thereto havinga series of spark gaps therein, the voltage across the spark gaps being insufficient to cause them to strike, an auxiliary circuit comprising a primary circuit and a secondary circuit coupled thereto, spark gap means in said primary circuit and means for applying the energy in said secondary circuit acrssat least one of saidv first-mentioned spark gaps 75\ whereby said iirst-mentioned spark gaps are caused to strike.

6. In a device of the class described, the combination of a source of voltage, a power circuit connected thereto having a series of spark gaps therein, the voltage across the gaps being insuiicient to cause them to strike, and an auxiliary lrcuit having spark gap means therein and comprising a primary circuit and secondary circuit coupled thereto for ionizing the air between certain of said series of gaps and to permit current from the power circuit to ow through the gaps, said spark gap means in said auxiliary circuit being in the primary circuit thereof, and

a condenser in the secondary `circuit to limit the current flowing therethrough,

'7. In a device of the class described, the combination of a source of voltage, a power circuit connected thereto, a series of liquid cooled adjustable quench 4spark gaps, in said power circuit having a total electrode capacitance not substantially greater than the capacitance between the sparking surfaces, the Voltage across the spark gaps being insufficient to cause them to strike, an auxiliary circuit comprising a primary circuit and a secondary circuit coupled thereto, spark gap means in said primary circuit and means fcr applying the energy in said secondary circuitv across at least one of said first mentioned spark gaps whereby said first mentioned spark gaps are caused to strike.

8. In a device of the class described, the combination of a source of voltage, a power circuit connected thereto, a series of liquid cooled spark gaps in said pov/er circuit comprising a series of pairs of substantially parallel sparking surfaces of substantial area, the sparking surfaces of each pair being slightly separated, the voltage across the spark gaps being insufficient to cause them to strike, an auxiliary circuit comprising a primary circuit and a secondary circuit coupled thereto, spark gap means in said primary circuit and means for` applying the energy in said secondary circuit across at least one of said first mentioned spark gaps whereby said iirst mentioned spark'gaps are caused to strike.

9. In a device of the class described, the combination of a source of electric voltage, a substantially balanced electric circuit having a spark gap therein, the voltage across the terminals of the spark gap being insucient to cause the spark gap to strike and an auxiliary circuit comprising a primary circuit and a secondary circuit coupled thereto, spark gap means in said primary circuit and means for applying the energy in said secondary circuit across said rst mentioned spark gap whereby said spark gap is caused to strike.

10. In a quench gap device, the combination of a support made of an insulating material recessed to permit tubes to extend therethrough, a plurality of aligned members having a passage therethrough mounted on said support, one of said `members being Xe-d in position and other members being adjustable to Vary their positions with respect to the fixed member, spark gap surfaces on the respective ends of the fixed member, spark gap surfaces onthe ends of the adjacent members retained by said support in substantially parallel relation to the sparking surfaces on the fixed member, and tubes associated with said passages and extending through said recessed support for flowing a cooling fluid in heat conducting relation to said fixed and adjustable members. i

ll. A liquid cooled adjustable quench gap, having a total electrode capacitance not substantially greater than the capacitance between the sparking surfaces, comprising a pair of substantially cylindrical members having parallel sparking surfaces of substantial area and substantially equal to the cross sectional area of the cylindrical members, means for flowing a liquid for cooling said surfaces, means effective upon said cylindrical members for retaining said surfaces in parallel relation, and means for moving the members and the surfaces toward and away from each other Without disturbing the parallel relation between the surfaces to vary the space between the surfaces.

12. A liquid cooled adjustable quench gap, having a total electrode capacitance not substantially greater than the capacitance between the sparking surfaces, comprising a pair of substantially parallel sparking surfaces of substantial area, means for flowing a liquid f-or cooling said surfaces, means for retaining said surfaces in parallel relation including resilient means cooperating to slidably hold one of said surfaces in position thereby to permit movement relative to the other surface, and means for moving said movable surface toward the other surface without disturbing their parallel relationship tedecrease the space between the surfaces.

13. In a spark gap device, the combination of an insulating base recessed to facilitate attachment of parts thereto, a fixed member mounted on said base having sparking surfaces at its respective ends, means extending through a recess in said base and slidably secured on the underside of the base, a member secured to said means and movably mounted at one end of said fixed member, a second means extending through a recess in said base and slidably securedto the underside of the base, a second member secured to said second means and movably mounted at the other end of said fixed member, each of said movable members having a sparking surface adjacent a sparking surface on said fixed member, means operatively connected to each of said movable members to move said movable members toward and away from said fixed member and metal tube means in heat conducting relation to said fixed and movable members for conducting cooling water to and from each of said members to cool said members and said sparking surfaces.

14. A liquid cooled adjustable quench gap, having a total electrode capacitance not substantially greater than the capacitance between the sparking surfaces, comprising a pair of members having substantially uniform cross-section and having parallel sparking surfaces of substantial area and substantially equal to the cross sectional area of the said members, means for flowing a liquid for cooling said surfaces, means effective upon said members for retaining said surfaces in parallel relation, and means for moving the members and the surfaces toward and away from each other without disturbing the parallel relation between the surfaces to vary the space between the surfaces.

EMIL R. CAPITA. 

